What the heck is Premenopause, Perimenopause and Postmenopause?

As defined by the World Health Organization, menopause is the permanent cessation of menstruation due to the loss of ovarian follicular activity . This definition uses both a symptom that can be identified by a woman (the end of menstruation) and a sign that can be measured (the loss of follicular activity results in changes in levels of hormones). Investigators have generally agreed to define menopause as the last menstrual period followed by at least twelve months of amenorrhea (no menstrual bleeding). The advantage of this definition is that it identifies a single, measurable variable within the climacteric transition. This definition makes it possible to compute median or mean ages at menopause for inter- and intrapopulation comparisons. The definition also allows one to delineate a clinically normal range in age at menopause (for example, ages forty to sixty). Finally, this definition enables clinicians to identify
women who are postmenopausal for medical “management.” But while thelast menstrual period is a clinically useful marker of an event, the average woman’s sense of the process of the menopausal transition is better described by the term “perimenopause,” a gray, difficult-to-define time period during which a woman wonders if each period of bleeding is the last.

K. I know thats too complicated so take this:

Stages and Definitions of the Menopause Transition

Premenopause: Regular cycling. Having experienced a menstrual period
during the two months prior to study.

Perimenopause: Irregular cycling. Having experienced a menstrual period
from three to eleven months prior to study.

Postmenopause: Having experienced the last menstrual period at least
twelve months prior to study

That said, women still perceive menopause to be a marker for the end of childbearing because most women have no other “window” into the state of their ability to conceive. The end of menstruation can, therefore, be an emotionladen event. Some women react to the cessation of menstruation with relief (no more birth control); others describe deep sadness because they can no longer bear children.